From 106b4a2a78b2a2f14885604891957b84bba502db Mon Sep 17 00:00:00 2001 From: Adrian Betschart Date: Fri, 11 Sep 2026 17:13:14 +0200 Subject: drm/amd/display: Try RGB before YCbCr 4:4:4 in stream validation amdgpu_dm_create_validate_stream_for_sink() walks encoding_order[] and uses the first encoding that validates. YCbCr 4:4:4 is listed before RGB, so an HDMI sink that advertises 4:4:4 gets YCbCr 4:4:4 whenever the "color format" property is left at AUTO, even though RGB fits the same link. That contradicts the documented AUTO behaviour for HDMI in enum drm_connector_color_format (RGB, falling back to YCbCr 4:2:0 only when the bandwidth is not available or the mode is 4:2:0-only), which the amdgpu implementation of the property also describes. It also leaves the "Broadcast RGB" property without effect on such sinks, since the quantization range it selects only applies to RGB output. Try RGB first. The mask still holds every encoding the sink supports, so a mode that cannot carry RGB falls back exactly as before. For reference, v7.2 picked RGB here unless YCbCr 4:4:4 was forced through debugfs, while earlier kernels picked YCbCr 4:4:4 for any HDMI sink that advertised it. Fixes: 0b0ff65d3ca1 ("drm/amd/display: Refactor stream validation") Suggested-by: Adolfo Rodrigues Assisted-by: Claude Code:claude-fable-5-1 Signed-off-by: Adrian Betschart Reviewed-by: Fangzhi Zuo Tested-by: Adolfo Rodrigues Tested-by: Daniel Wheeler Signed-off-by: Alex Deucher (cherry picked from commit 7de432bc753133764dc40d37f9388da56de251e7) --- Documentation/input/uinput.rst | 245 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 245 insertions(+) create mode 100644 Documentation/input/uinput.rst (limited to 'Documentation/input/uinput.rst') diff --git a/Documentation/input/uinput.rst b/Documentation/input/uinput.rst new file mode 100644 index 000000000..30fe80e32 --- /dev/null +++ b/Documentation/input/uinput.rst @@ -0,0 +1,245 @@ +============= +uinput module +============= + +Introduction +============ + +uinput is a kernel module that makes it possible to emulate input devices +from userspace. By writing to /dev/uinput (or /dev/input/uinput) device, a +process can create a virtual input device with specific capabilities. Once +this virtual device is created, the process can send events through it, +that will be delivered to userspace and in-kernel consumers. + +Interface +========= + +:: + + linux/uinput.h + +The uinput header defines ioctls to create, set up, and destroy virtual +devices. + +libevdev +======== + +libevdev is a wrapper library for evdev devices that provides interfaces to +create uinput devices and send events. libevdev is less error-prone than +accessing uinput directly, and should be considered for new software. + +For examples and more information about libevdev: +https://www.freedesktop.org/software/libevdev/doc/latest/ + +Examples +======== + +Keyboard events +--------------- + +This first example shows how to create a new virtual device, and how to +send a key event. All default imports and error handlers were removed for +the sake of simplicity. + +.. code-block:: c + + #include + + void emit(int fd, int type, int code, int val) + { + struct input_event ie; + + ie.type = type; + ie.code = code; + ie.value = val; + /* timestamp values below are ignored */ + ie.time.tv_sec = 0; + ie.time.tv_usec = 0; + + write(fd, &ie, sizeof(ie)); + } + + int main(void) + { + struct uinput_setup usetup; + + int fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK); + + + /* + * The ioctls below will enable the device that is about to be + * created, to pass key events, in this case the space key. + */ + ioctl(fd, UI_SET_EVBIT, EV_KEY); + ioctl(fd, UI_SET_KEYBIT, KEY_SPACE); + + memset(&usetup, 0, sizeof(usetup)); + usetup.id.bustype = BUS_USB; + usetup.id.vendor = 0x1234; /* sample vendor */ + usetup.id.product = 0x5678; /* sample product */ + strcpy(usetup.name, "Example device"); + + ioctl(fd, UI_DEV_SETUP, &usetup); + ioctl(fd, UI_DEV_CREATE); + + /* + * On UI_DEV_CREATE the kernel will create the device node for this + * device. We are inserting a pause here so that userspace has time + * to detect, initialize the new device, and can start listening to + * the event, otherwise it will not notice the event we are about + * to send. This pause is only needed in our example code! + */ + sleep(1); + + /* Key press, report the event, send key release, and report again */ + emit(fd, EV_KEY, KEY_SPACE, 1); + emit(fd, EV_SYN, SYN_REPORT, 0); + emit(fd, EV_KEY, KEY_SPACE, 0); + emit(fd, EV_SYN, SYN_REPORT, 0); + + /* + * Give userspace some time to read the events before we destroy the + * device with UI_DEV_DESTROY. + */ + sleep(1); + + ioctl(fd, UI_DEV_DESTROY); + close(fd); + + return 0; + } + +Mouse movements +--------------- + +This example shows how to create a virtual device that behaves like a physical +mouse. + +.. code-block:: c + + #include + + /* emit function is identical to of the first example */ + + int main(void) + { + struct uinput_setup usetup; + int i = 50; + + int fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK); + + /* enable mouse button left and relative events */ + ioctl(fd, UI_SET_EVBIT, EV_KEY); + ioctl(fd, UI_SET_KEYBIT, BTN_LEFT); + + ioctl(fd, UI_SET_EVBIT, EV_REL); + ioctl(fd, UI_SET_RELBIT, REL_X); + ioctl(fd, UI_SET_RELBIT, REL_Y); + + memset(&usetup, 0, sizeof(usetup)); + usetup.id.bustype = BUS_USB; + usetup.id.vendor = 0x1234; /* sample vendor */ + usetup.id.product = 0x5678; /* sample product */ + strcpy(usetup.name, "Example device"); + + ioctl(fd, UI_DEV_SETUP, &usetup); + ioctl(fd, UI_DEV_CREATE); + + /* + * On UI_DEV_CREATE the kernel will create the device node for this + * device. We are inserting a pause here so that userspace has time + * to detect, initialize the new device, and can start listening to + * the event, otherwise it will not notice the event we are about + * to send. This pause is only needed in our example code! + */ + sleep(1); + + /* Move the mouse diagonally, 5 units per axis */ + while (i--) { + emit(fd, EV_REL, REL_X, 5); + emit(fd, EV_REL, REL_Y, 5); + emit(fd, EV_SYN, SYN_REPORT, 0); + usleep(15000); + } + + /* + * Give userspace some time to read the events before we destroy the + * device with UI_DEV_DESTROY. + */ + sleep(1); + + ioctl(fd, UI_DEV_DESTROY); + close(fd); + + return 0; + } + + +uinput old interface +-------------------- + +Before uinput version 5, there wasn't a dedicated ioctl to set up a virtual +device. Programs supporting older versions of uinput interface need to fill +a uinput_user_dev structure and write it to the uinput file descriptor to +configure the new uinput device. New code should not use the old interface +but interact with uinput via ioctl calls, or use libevdev. + +.. code-block:: c + + #include + + /* emit function is identical to of the first example */ + + int main(void) + { + struct uinput_user_dev uud; + int version, rc, fd; + + fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK); + rc = ioctl(fd, UI_GET_VERSION, &version); + + if (rc == 0 && version >= 5) { + /* use UI_DEV_SETUP */ + return 0; + } + + /* + * The ioctls below will enable the device that is about to be + * created, to pass key events, in this case the space key. + */ + ioctl(fd, UI_SET_EVBIT, EV_KEY); + ioctl(fd, UI_SET_KEYBIT, KEY_SPACE); + + memset(&uud, 0, sizeof(uud)); + snprintf(uud.name, UINPUT_MAX_NAME_SIZE, "uinput old interface"); + write(fd, &uud, sizeof(uud)); + + ioctl(fd, UI_DEV_CREATE); + + /* + * On UI_DEV_CREATE the kernel will create the device node for this + * device. We are inserting a pause here so that userspace has time + * to detect, initialize the new device, and can start listening to + * the event, otherwise it will not notice the event we are about + * to send. This pause is only needed in our example code! + */ + sleep(1); + + /* Key press, report the event, send key release, and report again */ + emit(fd, EV_KEY, KEY_SPACE, 1); + emit(fd, EV_SYN, SYN_REPORT, 0); + emit(fd, EV_KEY, KEY_SPACE, 0); + emit(fd, EV_SYN, SYN_REPORT, 0); + + /* + * Give userspace some time to read the events before we destroy the + * device with UI_DEV_DESTROY. + */ + sleep(1); + + ioctl(fd, UI_DEV_DESTROY); + + close(fd); + return 0; + } + -- cgit v1.3.1